Optical recording medium, method for manufacturing the same, and optical information recording and reproducing device used with respect to the same

ABSTRACT

An optical disk has address recording sections each of which has a wobbled part of one of side walls of a groove. Each address recording section is formed by providing convexes of a groove in an adjacent land so as to widen the groove. With the wobbles thus provided in a concavo-convex form, address information is recorded. Besides, the address recording sections thus provided in the grooves are linearly disposed in radial directions of the optical disk. By thus arranging the optical disk on whose grooves and/or lands information is recorded, mixing of wobble frequency components in reproduced information signals does not occur, the sector method is applicable to the optical disk, and information signals of high quality can be obtained.

This application is a divisional of U.S. application Ser. No.08/890,401, filed Jul. 9, 1997, now U.S. Pat. No. 5,933,411, theteachings of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an optical recording medium to and fromwhich information is recorded and reproduced by the use of light, amethod for manufacturing the optical recording medium, and an opticalinformation recording and reproducing device used with respect to theoptical recording medium.

BACKGROUND OF THE INVENTION

A rapid technological innovation has recently been achieved as to theoptical recording medium to and from which signals are recorded andreproduced by the use of light. Numerous attempts have been madeparticularly to increase recording capacity, working out various elementtechnologies for this purpose.

Among such technologies there are those relating to a disk-shape mediumto which information is recorded, that is, a so-called optical disk. Theoptical disk usually has a configuration wherein a recording mediumlayer is provided on a substrate having tracks thereon. In this case, bymaking a light spot trace the tracks, the light spot is caused toaccurately follow lines of fine recording marks.

In the case of the optical disk, when tracks are formed on thesubstrate, address information of the tracks are also marked on thetracks at the same time. Specifically, pits indicating track numbers,sector numbers, etc., are formed on the tracks or between the tracks,and by reading them the address information can be obtained.

In another method for marking address information, wobbled grooves areused. To be more specific, as shown in FIG. 13, both side walls of agroove 101 provided on an optical disk (they are also side walls ofadjacent lands 102) are wobbled in a direction orthogonal to alongitudinal direction of the track (the method using such grooves ishereinafter referred to as both-sidewobble method). A wobble frequencyobtained therefrom is modulated by a certain method, and addressinformation is allocated to it. In this case, by setting the wobblefrequency higher than frequencies to which the light spot is capable offollowing, the light spot does not follow the wobble frequency duringtracking and wobble frequency components are always added to a trackingsignal. Therefore, by detecting the wobble frequency components, theaddress information can be obtained. Incidentally, as a method forincreasing the capacity of the optical disk, a land/groove recordingmethod has been proposed. Conventionally signals are recorded on eitherthe grooves or the lands between the grooves, but in contrast, the abovemethod is for recording information on both the grooves and lands. Inthis case, it is impossible to accurately record address information tolands 102 wobbled in a manner as shown in FIG. 13, since a width of theland 102 varies with wobbles of the two adjacent grooves 101.

As a method to solve this problem, a method using grooves one of whoseside walls is wobbled, that is, a single-side-wobble method, isdisclosed by the Japanese Publication for Laid-open Patent ApplicationNo.5-314538/1993 (Tokukaihei No.5-314538). The method is applied to anoptical disk having grooves 111 and lands 112 thereon wherein only oneside wall of each groove 111 is wobbled, as shown in FIG. 14, so thataddress information is recorded, using a wobble frequency obtained fromthe wobble.

However, in the case of the both-side-wobble method and thesingle-side-wobble method both, every groove (or land) has a wobbledside wall, that is, a portion being tracked always has a wobbled sidewall. Therefore, a reproduction signal of information includes wobblefrequency components since mixture of wobble frequency components occurswhen information signals are recorded or reproduced. As a result, signalquality deteriorates.

Besides, due to the above-mentioned signal mixture, it is necessary toset the wobble frequency in a frequency band different from thefrequency band for the information signal, and hence the wobblefrequency is set much lower than the frequency of the informationsignal. Therefore, the spatial wavelength of the wobble frequencybecomes long, and accordingly each domain has to be long so as toexpress each piece of address information. As a result, making divisionsbetween addresses clear and precise is failed.

This does not signifies much in the case of signals to be continuouslytransmitted, such as video signals or sound signals. However, in thecase where an optical disk is used as a memory of a computing devicewherein signal transmission is frequently carried out, signals aregrouped into blocks when transmitted, and it is necessary to arrangedata by a so-called sector method. In this case, the above matterbecomes a serious problem.

Besides, since the width of the grooves or the lands varies in someareas, there arise a problem that the beam spot may have an offset, andbesides, a problem that the offset is difficult to correct.

There are more methods for providing address information in the casewhere the land/groove recording method is used. For example, anexclusive address method and a common address method are reported by"Nikkei Electronics" (Nov. 6, 1995, p. 168).

The former is a method whereby at every sector in both the lands andgrooves, a pre-pit is provided exclusively for the sector. However,since it is necessary that the pit width is sufficiently narrower thanthe track width, the pre-pits cannot be formed by the use of a lightbeam used for forming the tracks. Thus, this method has a defect ofmaking it difficult to manufacture optical disks.

By the latter, that is, the common address method, as shown in FIG. 15,pit series 123 are provided on borders between grooves 121 and lands 122so that each pair of adjacent groove 121 and land 122 share pit series123. In this case, a light spot 124 always tracks off the center of pitseries 123 when reproducing the pit, during both the tracking operationswith respect to the grooves 121 and lands 122. Therefore, there arises aproblem that the signal quality is low.

Further, when the light spot 124 passes the pit series 123, the lightspot 124 does not tracks on a center line of the pit series 123, therebycausing a great off-set to be added to the tracking signal. Since thepits are intermittently provided, the tracking signal obtained from thepits is also intermittent, but it comes to a great off-set on theaverage.

A tracking servo system usually does not respond to the tracking signalitself obtained from the individual pit since the pit frequency issufficiently higher than a frequency band of the tracking servo system.However, since the pit region is considerably long in the present case,the tracking signal is averaged through out the pit region, therebybecoming a signal having a great off-set, to which the servo systemresponds. As a result, a signal having great spikes is generated whenthe light spot passes through the pit region. An actuator of thetracking servo system responds to the signal having spikes in the casewhere the pit region is considerably long, thereby causing a problem oftransient response, which reversely affects the signal recording andreproduction.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an optical recordingmedium which has the following properties when the land/groove recordingmethod is applied: (1) mixing of wobble frequency components in theinformation signals does not occur; (2) the sector method is applicablethereto without difficulties; and (3) information signals of highquality is reproduced. It is also the object of the present invention toprovide a method for manufacturing the optical recording medium and toprovide a n optical information recording and reproducing device for theuse with respect to the optical recording medium.

To achieve the above object, an optical recording medium of the presentinvention, which has a plurality of lands and grooves between the lands,each of the lands and the grooves serving as a track on which a lightbeam is projected for recording, reproducing, and erasing information,is characterized in that each track has at least one wobble section sothat address information is recorded therein, the wobble section havinga dispersively wobbled side wall of either the groove or the land.

With the aforementioned arrangement, in the case where information isrecorded in regions other than the region corresponding to the wobblesection, the mixing of a wobble signal in an information signal does notoccur, thereby causing no deterioration of signal quality. Therefore,information signals of high quality can be obtained. On the other hand,by recording address information by using wobbles, address signals canbe surely detected without affecting the information signals, duringrecording, reproducing, and erasing operations.

Furthermore, in the case where the optical recording medium is anoptical disk, the wobble sections provided on the tracks on the opticaldisk may be linearly disposed in a radial direction of the optical disk.

In the above arrangement, regions other than those corresponding to thewobble sections, that is, regions where information is recorded, areadjusted in radial directions of the optical disk since the wobblesections are linearly disposed in radial directions of the optical disk.Therefore, timings to detect the address signals are taken withprecision, thereby enabling secure detection of the address signalsduring access operations to other tracks. As a result, speedy access isachieved.

Furthermore, in the case where the optical recording medium is anoptical disk, the wobble sections provided on adjacent tracks may bedisposed at respective positions in different directions from a centerof the optical disk.

With the above arrangement, it is possible to provide the wobblesections in accordance with a line velocity, and make the recordingdensity substantially constant from the innermost track to the outermosttrack. As a result, the recording capacity can be extended.

An optical information recording and reproducing device of the presentinvention is characterized in comprising (1) a photodetector fordetecting reflected light obtained by projecting a light beam on theoptical recording medium, and (2) an operational unit for detecting atracking signal in accordance with a signal supplied from thephotodetector and extracting wobble frequency components due to thewobble sections out of the tracking signal.

In the foregoing arrangement, the tracking signal is obtained byprojecting the light beam onto the optical recording medium. Then, thewobble frequency components are extracted out of the tracking signal. Bydoing so, the wobble signals are detected without affecting theinformation signals.

The optical information recording and reproducing device of the presentinvention may be arranged so as to comprise (1) a photodetector fordetecting a quantity of reflected light obtained by projecting a lightbeam on the optical recording medium, and (2) an operational unit fordetecting changes in the quantity of the reflected light and extractingwobble frequency components due to the wobble section.

In the above arrangement, changes in the width of the groove or the landcause changes in the quantity of the reflected light due to diffractioneffects. Therefore, by detecting the quantity of the reflected light,the wobble frequency components can be extracted. Therefore, thedetecting system for detecting the tracking signals is not required tobe capable of highspeed response. Consequently, it is possible toprovide an inexpensive detecting system.

A method for manufacturing an optical recording medium of the presentinvention is characterized in comprising the steps of (a) providing aphotosensitive material over a substrate, and (b) selectively exposingthe photosensitive material in a shape of the wobble section byprojecting two light beams with a distance therebetween in a directionorthogonal to a lengthwise direction of the track and swinging one ofthe two light beams in the direction orthogonal to the lengthwisedirection of the track.

By the aforementioned method, the amplitude of the wobble is freelycontrolled by changing the amount of the shift of the light beam in thedirection orthogonal to the lengthwise direction of the tracks.Therefore, a shape of the wobble section is freely controlled.Accordingly, the wobble sections where only one side wall of either thegroove or the land is wobbled can be easily formed.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an arrangement of an opticaldisk in accordance with a first embodiment of the present invention.

FIG. 2(a) is a view illustrating an arrangement of an opticalinformation recording and reproducing device to be used with respect tothe optical disk.

FIG. 2(b) is a plan view illustrating a light receiving surface of aphotodetector provided in the optical information recording andreproducing device.

FIG. 3 is a plan view illustrating an example of an arrangement ofaddress recording sections on the optical disk.

FIG. 4 is a plan view illustrating an example of a shape of the addressrecording sections.

FIG. 5 is a plan view illustrating another example of the shape of theaddress recording sections.

FIG. 6 is a plan view illustrating still another example of the shape ofthe address recording sections.

FIG. 7 is a view illustrating how a tracking operation is performed withrespect to the address recording section shown in FIG. 6.

FIG. 8 is a waveform chart of a tracking signal obtained by the trackingoperation illustrated in FIG. 7.

FIG. 9 is a waveform chart illustrating quantities of reflected lightobtained from the optical disk by the tracking operations illustrated inFIG. 7.

FIG. 10 is a perspective view illustrating another arrangement of theaddress recording sections.

FIG. 11 is a view illustrating an arrangement of a recording device usedin a step of exposing a photoresist.

FIG. 12 is an explanatory view showing a method for forming the addressrecording sections by the use of the recording device.

FIG. 13 is a plan view illustrating grooves in a conventional opticaldisk, both side walls of each groove being wobbled.

FIG. 14 is a plan view illustrating grooves in another conventionaloptical disk, one of side walls of each groove being wobbled.

FIG. 15 is a plan view illustrating how a common address method isapplied with respect to a conventional optical disk.

FIG. 16 is a plan view illustrating an arrangement of an optical disksubstrate in accordance with any one of second through sixth embodimentsof the present invention.

FIG. 17 is a cross section of the optical disk substrate.

FIGS. 18(a) through 18(e) are cross sections illustrating steps of amanufacturing process of the optical disk substrate.

FIG. 19 is a view illustrating an arrangement of a manufacturing deviceof the optical disk substrate.

FIGS. 20(a) through 20(f) are cross sections illustrating steps ofanother manufacturing process of the optical disk substrate.

FIG. 21 is a cross section illustrating an arrangement of an opticaldisk using the optical disk substrate.

FIG. 22 is a cross section illustrating an arrangement of anotheroptical disk using the optical disk substrate.

FIG. 23 is a cross section illustrating an arrangement of still anotheroptical disk using the optical disk substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

The following description will discuss a first embodiment of the presentinvention, while referring to FIGS. 1 through 12.

An optical information recording and reproducing device in accordancewith the present embodiment is as follows. As illustrated in FIG. 2(a),the optical information recording and reproducing device has a detectingsystem for reproducing information recorded in an optical disk (opticalrecording medium) 1.

A light beam emitted by a semiconductor laser 2 of the detecting systemis parallelized by a collimating lens 3, then passes through a beamsplitter 4. Thereafter, the light beam is converged by an objective lens5 onto the optical disk 1. Reflected light from the optical disk 1returns to the beam splitter 4 through the objective lens 5. Thereafter,the light is deflected by the beam splitter 4 and enters a beam splitter6. The light is split into two light fluxes by the beam splitter 6, andone of the two is converged onto a photodetector 9 via a converging lens7 and a cylindrical lens 8.

As shown in FIG. 2 (b) , the photodetector 9 is a servo-use detectorhaving quaternary light receiving surfaces 9a, 9b, 9c, and 9d, each ofwhich is connected to an operational circuit (operational unit) 10.Herein, due to the cylindrical lens 8, a shape of a light spot formed onthe light receiving surfaces 9a, 9b, 9c, and 9d changes to an oval shapewhich varies with focus irregularities. Therefore, let quantities ofsignals obtained at the light receiving surfaces 9a, 9b, 9c, and 9d beA, B, C, and D, respectively, then a focus error signal is obtained bycalculating A+D-(B+C) in the operational circuit 10.

In the case where a direction (direction indicated by an arrow) from thelight receiving surface 9c to the light receiving surface 9a in FIG.2(b) conforms to a track direction, a track error signal is found bycalculating A+C-(B+D). This calculation is also performed by theoperational circuit 10. Based on a tracking signal obtained from thetrack error signal, a tracking operation is carried out with respect toa track on the optical disk 1.

On the other hand, the other one of the light fluxes which is nottransmitted but reflected by the beam splitter 6 is projected on apolarizing beam splitter 12 through a converging lens 11, and is dividedinto two light fluxes by the polarizing beam splitter 12. The lightfluxes thus obtained are converged onto photodetectors 13 and 14,respectively. Differential reproduction is carried out with respect tooutputs of the photodetectors 13 and 14 by an operational amplifier 15,and as a result information recorded in the optical disk 1 is obtainedin the form of magneto-optical signals (information signals).

The reflected light from the optical disk 1 is detected either (1) bycomputing a sum of the light quantities (=A+B+C+D) detected by thequarternary light detecting surfaces of the photodetector 9 or (2) byusing an amplifier (operational unit) 16 which computes a sum of outputsof the photodetectors 13 and 14 detecting the magneto-optical signals.

Note that the above-described arrangement of the optical informationrecording and reproducing device is merely one example, and anarrangement having the same function can be achieved with variousoptical parts.

FIG. 1 illustrates a configuration of the optical disk 1 having addressrecording sections (wobble sections) 24 which characterize the presentinvention. The optical disk 1 is composed of a transparent substrate 20,and a recording medium layer 23 provided on the transparent substrate20. On the transparent substrate 20, grooves 21 and lands 22 each ofwhich serves as a track are provided in a concentric or seoieral form.Information signals are recorded in the recording medium layer 23.

The light beam converged by the objective lens 5 forms light spots s₁and s₂ on the land 22 and the groove 21, respectively. In other words,the light spot s₂ formed by the light beam follows the groove 21, whilethe light spot s₁ follows the land 22.

The recording medium layer 23 is made of either (1) a material such asrare earth-transition metal alloy used for magneto-optical recording or(2) a phase transition material used in the case where signals arerecorded by utilizing the crystal-amorphous phase transition due totemperature changes. The recording medium layer 23, which du e to thestructure thereof exhibits a super resolution effect, is capable ofreproducing a recording mark smaller than the light spot. Therefore,even though information is recorded on the grooves 21 and the lands 22both, the information can be reproduced without crosstalk betweenrespective signals. As a result, information can be recorded on thegrooves 21 and the lands 22 both, resulting in enhancement of therecording density.

On a part of one of side walls of each groove 21 (which is one of sidewalls of each land 22) , which constitutes a border between the groove21 and an adjacent land 22, there is provided an address recordingsection 24. As illustrated in FIG. 4 which is a plan view of FIG. 1, ineach address recording section 24, the groove 21 has a plurality ofconvexes 24a therein (which constitute concaves in the land 22) , and asa result the side wall of the groove 21 wobbles, having concaves andconvexes in a radial direction of the optical disk 1. In other words,the groove 21 is widened so as to form the convexes 24a. Addressinformation is recorded by utilizing such a wobble of the side wall.Herein, a frequency (wobble frequency) of changes of the side wall widthin the address recording section 24 is set higher than a responsefrequency of the tracking servo system.

Positions of the address recording sections 24 thus provided in all thegrooves 21 are adjusted in radial directions of the optical disk 1. Bythus arranging the address recording sections 24, regions 26 as shown inFIG. 3 are formed. A single region 26 is, or a plurality of regions 26are, radially provided, and information recording sections 25 areprovided between the regions 26. Therefore, the tracking operation iscarried out alternately with respect to the regions 26 (addressrecording sections 24) and the information recording sections 25 whilethe light spot follows one track.

In the case where the address recording sections 24 are dispersivelyprovided in the above-described manner, information recorded in oneinformation recording section 25 following to one address recordingsection 24 is dealt with as a unit, and this configuration (so-calledsector configuration) is suitable for a memory for the use in acomputing device which frequently transfers information to and from thememory. In other words, with this configuration, timings for detectingaddress signals can be accurately taken, and the address signals aredetected without failure during an access operation to another track,thereby ensuring speedy access. Note that the number of the regions 26may be determined so as to match the purpose.

The above description explains an example wherein the address recordingsections 24 are linearly provided in the radial direction of the opticaldisk 1 as illustrated in FIG. 3, thereby forming the regions 26, butaddress recording sections 54 may be provided in different directionsfrom the center of the optical disk, as illustrated in FIG. 10. In otherwords, the address recording sections 54, in each of which wobble isformed on one of side walls of a groove 51 (which is one of side wallsof a land 52), are not linearly provided in any radial direction of theoptical disk.

This configuration is applicable to a format such as CLV (constant linevelocity), ZCAV (zoned constant angular velocity), and ZCLV (zonedconstant line velocity). In other words, this configuration isapplicable to a format wherein the address recording sections are notdisposed on a line in a radial direction. Therefore, the addressrecording sections can be disposed in accordance with a line velocity,and it is possible to make the recording density substantially constantfrom the innermost track to the outermost track. As a result, it ispossible to extend the recording capacity of the optical disk.

In the above description, referring to FIG. 4, the case wherein theaddress signals are recorded by changing the width of the grooves 21 sothat the grooves 21 are widened in the address recording sections 24 istaken as an example. But the grooves 21 may be narrowed in the addressrecording sections 24 so that the address signals are recorded thereon.In other words, in a configuration wherein grooves 31 and lands 32 areprovided, the lands 32 are widened in address recording sections 34, asillustrated in FIG. 5.

Alternatively, as illustrated in FIG. 6, in an optical disk whereingrooves 41 and lands 42 are provided, address recording sections 44 maybe arranged so that wobbles extend over both the groove 41 and the land42. To be more specific, convexes 41a and concaves 41b are provided onone of side walls of the groove 41. Herein, as illustrated in FIG. 7,the groove 41 is widened by a width `a` so as to form the convex 41a,while the groove 41 is narrowed by a width `b` so as to form the concave41b (a width like a width `a` or `b` by which the groove (or land) isnarrowed or widened so as to form a concave or a convex constituting awobble is hereinafter referred to as wobble amplitude). Herein needlessto say, the optical disk 1 may have the same configuration as that inFIG. 6 except that 41 represents lands while 42 represents grooves inthis case.

Reproduction of signals from the address recording section 44 shown inFIG. 7 is illustrated in FIG. 8.

Assume that the light spot S follows a center line C₁ which links pointsof a width center of the groove 41, relatively proceeding in a directionindicated an arrow in the figure. A tracking signal obtained in thisoperation is as shown in FIG. 8. To be more specific, since the trackingoperation is performed by the tracking servo system, the track errorsignal becomes virtually zero in regions other than the addressrecording section 44, while in the address recording section 44 itchanges in accordance with changes in the width of the groove 41.

The reason is that since the wobble frequency of the address recordingsection 44 is set higher than the response frequency of the servosystem, the servo system does not respond to the wobble frequency whenthe address recording section 44 is tracked, thereby resulting in thatthe track error signal is generated. When tracking the address recordingsection 44, the light spot S traces not the center line C, but a linewhich links points at a center of an average width of the addressrecording section 44.

An amplitude of the track error signal in the address recording section44, if converted into a track width, is a/2 on one side plus b/2 on theother side. This is because the track width changes by `a` and `b`,respectively, in FIG. 7, and shifts of the light spot S from the centerline in the address recording section 44 are 1/2 of the changes in thetrack width.

Besides, the following can be observed: in the case where (1) a DCcomponent of the address signal itself, recorded in the addressrecording section 44, is zero and (2) as a geometric condition of theaddress recording section 44, the wobble amplitudes `a` and `b` are setso that `a`=`b`, an average of the track error signal is zero, nooff-set can be caused in the track error signal when the light spot Spasses through the address recording section 44.

Thus, by taking out the wobble frequency component out of the trackingsignal, it is possible to detect the address signal without affectingthe information signal.

Note that the optical information recording and reproducing device mayhave an arrangement wherein changes in quantity of the reflected lightdetected by photodetector 9 or the photodetectors 13 and 14 is used soas to obtain the address signal. The quantity of reflected light fromthe address recording section 44 of FIG. 7 is shown in FIG. 9.

Normally, since the quantity of the reflected light decreases as thegroove becomes narrower due to the diffraction effect of the groove, thequantity of the reflected light from a narrow portion of the groove issmall whereas that from a wide portion of the groove is great.Therefore, the quantity of the reflected light from the addressrecording section 44 having a wobble with wobble amplitudes of `a` and`b` changes as illustrated in FIG. 9. Thus, it is possible to obtain theaddress signal from the address recording section 44 not by detectingthe track error signal but by detecting the quantity of the reflectedlight.

In this case, there is no need to detect the track error signal at ahigh speed. Therefore, there is no need to arrange the operationalcircuit 10 so as to be capable of quick response. The signal frequencyband of the servo system normally falls in a range of several tens toseveral hundreds kHz since it depends on a response speed of an actuatoror the like, whereas the information signal frequency band falls in arange of several MHz to several tens MHz, and systems to detect thesesignals are arranged so as to correspond to the frequency bands.Therefore, in the case where high-speed signal detection is carried outby the use of a detecting system of the servo system, the detectingsystem comes to have excessive quality of performance. Therefore, in thecase where the address signal is obtained by detecting the quantity ofthe reflected light, only a detector for detecting the total quantity oflight (photodetectors 13 and 14 in the case of FIG. 2(a)) is required tohave an amplifier 16 capable of high-speed detection. As a result, thedetecting system is simplified, and hence does not come to haveexcessive quality.

As described above, the optical disk of the present embodiment isarranged so that each track has one or more address recording sectionswherein one of side walls of the groove or the land is dispersivelywobbled. Herein, in the case where it is arranged so that informationsignals are not to be recorded in the address recording sections, it ispossible to make a wobble amplitude of the wobbled side wall of theaddress recording section considerably greater than any conventionalwobble amplitude. The reason is as follows: since influences of thewobble signal on the information signal can be neglected in the casewhere information is not to be recorded in the address recordingsection, the wobble amplitude of the side wall is allowed to be great sothat a wobble signal clear enough can be obtained.

For example, in a conventional optical disk wherein grooves aremeandered, it is necessary that the wobble amplitude is not more thanabout 50 nm (about 5 to 6 percent of the groove width in the case wherethe groove is 0.8 μm wide), but in the present embodiment there is noneed to suppress the wobble to such a degree. As illustrated in FIG. 7,the wobble amplitude may be increased up to about 50 percent of thegroove width (for example, up to about 0.4 μm in the case where thegroove is 0.8 μm wide) . The same is applicable to the address recordingsections arranged as shown in FIG. 4 or FIG. 5.

In short, in the case where the wobble amplitude is about 5 to 50percent of the groove width, it is possible to detect the wobble signalwithout affecting the information signals. By thus increasing the wobbleamplitude, the liability of signals is enhanced, while an error rate inreproduction of address signals is lowered.

An arrangement in the other way around is also applicable, that is, thewobble amplitudes in the address recording sections may be decreased sothat information signals may be recorded in the address recordingsections. In this case, the recording capacity is extended since theaddress recording sections are also used as information recordingsections.

In the description of the present embodiment, an example whereininformation is recorded on both the grooves and lands is described, butinformation may be recorded either on the grooves or on the lands.However, as described above, it is preferable that both the grooves andlands are used for recording information so as to achieve a greaterrecording capacity.

The following description will explain a method for manufacturing anoptical disk substrate in accordance with the present embodiment.

First, by projecting a light beam on an original disk (substrate) onwhich a photoresist (photosensitive substance) has been provided,desired patterns of grooves, lands, pits, and the like, are recorded inthe photoresist. By developing the patterns, removing unnecessaryportions of the photoresist, and plating the photoresist with metal suchas nickel, the patterns recorded in the photoresist are transferred onthe plating film.

The plating film is removed from the original disk, so as to be madeinto a stamper. By molding plastic by the use of the stamper as a mold,an optical disk substrate having desired patterns such as grooves,lands, pits, and the like, is manufactured. A recording medium layer isformed on the substrate, and the optical disk described above iscompleted.

FIG. 11 shows an example of a recording device for recording the desiredpatterns in the photoresist.

The recording device has an argon laser 60 with which the photoresist onthe original disk 73 to light is exposed. The light beam of the argonlaser 60 is reflected by a mirror 61, and enters the beam splitter 62.The light beam is divided by the beam splitter 62 into two light beams,and one of them is guided to a light modulator 65a through a convex lens64a for conversion. The light beam proceeds to a light deflector 67a viathe light modulator 65 and a convex lens 66a, and a plane ofpolarization of the light beam is revolved through an angle of 90° by a1/2 retardation plate 68. Thereafter the light beam enters a polarizingbeam splitter 69.

On the other hand, the other one of the two light beams obtained as aresult of division by the beam splitter 62 proceeds to the polarizingbeam splitter 69 via a mirror 63, a convex lens 64b, a light modulator65b, a convex lens 66b, a light deflector 67b, and a mirror 70. The twolight beams are synthesized by the polarizing beam splitter 69.

The two light beams are guided to an objective lens 72 via a mirror 71,and are projected on a surface of the original disk 73 on which thephotoresist is provided. The original disk 73 is turned around by aspindle 74, while the objective lens 72 is driven in a radial direction(indicated by an arrow in the figure) of the original disk 73. As aresult, tracks are recorded thereon in a spiral or concentric form.

Here, since the light beam is divided into two and thereafter the twolight beams are synthesized and enter the objective lens 72, two lightspots are formed on the original disk 73. Besides, since the lightmodulators 65a and 65b and the light deflectors 67a and 67b arerespectively provided on optical paths of the two light beams,modulation and deflection can be carried out with respect to therespective light beams.

Referring to FIG. 12, a method for recording patterns on the originaldisk 73 will be described below.

When grooves 81 are to be recorded, two light spots S₃ and S₄ arearranged so as to be lined in a direction orthogonal to a lengthwisedirection of the tracks (i.e., in the radial direction of the originaldisk 73) so that a desired groove width is obtained. To record anaddress recording section 84, the following steps are carried out. Torecord a narrow portion of the groove 81, only the spot S₄ is used. Onthe other hand, to record a wide portion of the groove 81, both thelight spots S₃ and S₄ are used, with the light spot S₃ shifted in aradial direction of the original disk 73. This set of steps is repeatedin accordance with an address signal, and as a result the addressrecording section 84 is formed.

It is possible to shift the light spot S₃ in the radial direction by theuse of the light deflector 67a (or the light deflector 67b) shown inFIG. 11. By this method, the shape of the side wall of either the groove81 or the land 82 in the address recording section 84 is freelycontrolled. In other words, by changing an amount of the shift of thelight spot in the radial direction of the original disk 73, the wobbleamplitudes in the address recording section 84 are freely controlled.

Second Embodiment

The following description will explain an embodiment of an optical disksubstrate of the present invention, while referring to FIGS. 16 through20.

On an optical disk substrate 205 used in the present embodiment, thereare provided a region (wobble section) wherein one wobbled side wall201a is provided as one of side walls of each tracking-use groove 201and a region 201b wherein non-wobbled side wall is provided as one ofside walls of each tracking-use groove 201, as illustrated by a planview of FIG. 16 and a radial-direction cross-section of FIG. 17. Thegrooves 201 are formed in a spiral form or in a concentric form. Eacharea between the grooves 201 is called a land 202, and a width of theland 202 is set substantially equal to the width of the groove 201.

The side walls 201a are wobbled in a radial direction of the opticaldisk substrate 205 and the optical disk in accordance with addressinformation, and a wobble frequency thereof is set higher than afollow-up frequencies of a tracking servo system, and lower than arecording frequency.

A track which a recording/reproduction-use light spot 204 is made tofollow is easily switched from the groove 201 to the land 202 or viceversa, only by inverting a polarity of a tracking signal. The trackingsignal is obtained by, for example, the push-pull method. The addressinformation is obtained by extracting components of the wobble frequencyof the side wall 201a from a tracking signal.

To be more specific, when the light spot 204 is made to follow, forexample, the groove 201, the light spot 204 actually follows a centerline 204a running on a substantial center of an average width of thegroove 201, since the wobble frequency is higher than the follow-upfrequency of the tracking system. For this reason, there always occurs atracking error corresponding to a half of a wobble amplitude of thegroove 201. Therefore, by extracting the tracking error from thetracking signal, signal components of the wobble frequency can beobtained. This also applies to the case where the light spot 204 is madeto follow the land 202. It should be noted that information recordedthereon and the address information can be separated since the wobblefrequency is set lower than the recording frequencies, as describedabove.

Since the tracking error is half of the wobble amplitude, it isnecessary to double the wobble amplitude in order to obtain the samesignal components as those in the case where both the side walls of thegroove 201 are wobbled. However, in the case where the width of thegroove 201 and the width of the land 202 are 0.8 μm and 0.8 μm,respectively, a signal obtained is 1.4 times as large as that in thecases where the widths are 1.2 μm and 0.4 μm, 1.8 times as large as thatin the case where the widths are 1.3 μm and 0.3 μm, and 1.2 times aslarge as that in the case where the widths are 1.1 μm and 0.5 μm.Therefore, the wobble amplitude may be actually set about 1.4 (=2/1.4)times, 1.1 (=2/1.8) times, and 1.2 (=2/1.2) times, respectively.

Therefore, if the wobble amplitude in the case where both the side wallsare wobbled is ±30 nm, the wobble amplitude in the case where the oneside wall is wobbled may be set in a range of ±35 nm to ±50 nm.

In the case where the optical disk substrate 205 of the presentembodiment is used, the light spot 204, if having a diameter set largerthan a track pitch and less than twice the track pitch, does notirradiate two wobbled side walls 201a at a time. As a result accurateaddress information is obtained.

Address information of the groove 201 coincides with address informationof an adjacent land 202 sharing the wobbled side wall 201a with thegroove 201. However, designation of a track, either the groove 201 orthe land 202, is carried out just by inverting the polarity of thetracking signal. Therefore, selection of a specific track can be carriedout without difficulty.

In the aforementioned present embodiment , the wobble frequencycomponents are extracted from the tracking signal, but signal componentsof the wobble frequency may be extracted from changes in a quantity ofreflected light from the optical disk. To be more specific, reflectedlight from a portion where the groove 201 or the land 202 is narrow isweak, whereas reflected light from a portion where the groove 201 or theland 202 is wide is strong. Therefore, by extracting changes in thequantity of the reflected light of the recording/reproduction-use lightspot 204, the signal components of the wobble frequency can be obtained.

Next, referring to FIGS. 18(a) through 18(e), the following descriptionwill discuss a manufacturing process of the optical disk substrate 205.

First, as illustrated in FIG. 18(a), photoresist 206 is applied to oneside of a glass substrate 250.

Next, as illustrated in FIG. 18(b), a laser beam is converged by anobjective lens 207 onto the photoresist 206 so that the photoresist 206is exposed so as to form desired patterns of grooves 201.

As illustrated in FIG. 18(c), the exposed photoresist 206 is developedand removed, and subsequently, the desired patterns are formed by theresidual photoresist 206.

As illustrated in FIG. 18(d), the glass substrate 250 and thephotoresist 206 are etched by a dry etching or wet etching process sothat the desired patterns are formed in the glass substrate 250.

As illustrated in FIG. 18(e), the residual photoresist 206 is removed byan ashing process so that the optical disk substrate 205 is complete.

FIG. 19 illustrates a device for exposing the photoresist 206 in apattern of the groove 201.

The device has a laser beam source 211a for exposing the photoresist 206and a laser beam source 211b used for focalizing the objective lens 207.For example, an Ar laser is used as the laser beam source 211a, while anHe-Ne laser is used as the laser beam source 211b.

A laser beam from the laser beam source 211a is processed by a noisesuppressing device 212a so that optical noises are reduced, andthereafter, the light is reflected by mirrors 219 and 220 and is dividedinto two by a beam splitter 231. The two light fluxes thus obtainedenter light modulators 222a and 222b. As the light modulators 222a and222b, acoustooptic elements, for example, may be used. In this case, apair of converging lenses 221a and a pair of converging lenses 221b areprovided before and behind the light modulators 222a and 222b,respectively.

The laser beam having passed through the light modulator 222a enters alight deflector 223, and thereafter, it is reflected by a prism mirror233 in a right angle direction. As the light deflector 223, anelectro-optical element, or an acoustooptic element, for example, isused, so as to change a proceeding direction of the laser beam. On theother hand, the laser beam having passed through the light modulator222b enters a (1/2) retardation plate 232, where a plane of polarizationof the laser beam is revolved through an angle of 90°.

Thereafter, the laser beam is expanded by a beam expander 224 so as tohave an appropriate beam diameter, and then, a two-color mirror 215makes the laser beam enter the objective lens 207. The objective lens207 converges the laser beam so that the laser beam forms anexposure-use light spot on the photoresist 206 on the glass substrate250.

Note that the light modulators 222a and 222b, the light deflectors 223,and the beam expander 224 are controlled by drivers 225a, 225b, 226, and227, respectively.

On the other hand, the laser beam from the laser beam source 211b isprocessed by the noise suppressing device 212b so that optical noisesare reduced, then proceeds to the objective lens 207 via a lightdeflecting beam splitter 213, a (1/4) retardation plate 214, and thetwo-color mirror 215. By the objective lens 207, the laser beam isconverged on the photoresist 206 on the glass substrate 250.

Reflected light therefrom is again converged by the objective lens 207,passes through the two-color mirror 215, the (1/4) retardation plate214, and the light deflecting beam splitter 213, and then, it isconverged by an objective lens 216 and a cylindrical lens 217 on aphotodetector 218. In response to signals from the photodetector 218,the focus servo system drives the objective lens 207 in a focusdirection, whereby the objective lens 207 is focalized at thephotoresist 206 on the glass substrate 250 which is rotated by a spindlemotor.

In the above-described arrangement, positioning of the light beam spotis carried out. To be more specific, a DC voltage applied to the lightdeflector 223 and a setting angle of the prism mirror 233 are adjustedby the driver 226 so that a two light spots are formed with apredetermined average distance therebetween in the radial direction.Thereafter, only in regions where one of the side walls of the grooveshould be wobbled in accordance with address information, a voltageresulting on superimposing a signal voltage of the wobble frequency onthe aforementioned DC voltage is applied to the light deflector 223 bythe driver 226. By doing so, regions where only one side wall of thegroove is wobbled in accordance with address information are formed.

Note that the light spots are turned on and off by applying voltages tothe light modulators 222a and 222b by the drivers 225a and 225b,respectively.

The optical disk substrate 205 of the present embodiment is not limitedto the aforementioned one. Instead of this, any one made by plasticresin through the injection molding or the injection pressure molding bythe use of a stamper manufactured through steps illustrated in FIGS.20(a) through 20(f) may be used.

As illustrated in FIG. 20(a), photoresist 206 is applied to one surfaceof a glass substrate 250.

Next, as illustrated in FIG. 20(b), a laser beam is converged by anobjective lens 207 onto the photoresist 206 so that the photoresist 206is exposed so as to form desired patterns of the grooves 201.

As illustrated in FIG. 20 (c), the exposed photoresist 206 is developedand removed, and as a result, the desired patterns are formed by theresidual photoresist 206.

Thereafter, as shown in FIG. 20(d), a conductive thin film 208 is formedon the patterns made of the photoresist 206 by sputtering, electrolessplating or other methods.

Then, as illustrated in FIG. 20(e), a metal layer 209 is formed on thethin-film 208 by electrocasting or other methods.

Finally, as shown in FIG. 20(f) , the thin-film 208 and the metal layer209 are separated from the photoresist 206 and the glass substrate 250.The thin-film 208 and the metal layer 209 thus separated therefrom arecalled a stamper 210.

Here, Ni, Ta, Cr or an alloy of these materials is used as the materialof the thin-film 208, or a composite film of these materials is applied,and Ni, Ta, Cr or an alloy of these materials is also used as thematerial of the metal layer 209, or a composite film of these materialsis applied.

By using the above-mentioned stamper 210, an optical disk substrate 205,made of plastic, is manufactured through injection molding or injectionpressure molding. Thermoplastic resins, such as polycarbonate resin,acryl resin, ethylene resin, ester resin, nylon resin, or APO, are usedas the plastic material.

A method for manufacturing the stamper 210 of the present embodiment isnot limited to the aforementioned method, but another method using amask original disk produced so that one side wall 201a is wobbled ineach groove may be used.

In addition, materials of the optical disk substrate 205 and a methodfor manufacturing the optical disk substrate 205 are not limited tothose mentioned above.

Note that in the above description the address information is obtainedby extracting the signal components of the wobble frequency of the sidewall, but the address information may be obtained by reading shapes andnumber of wobbles. By doing so, there is no need to change the wobblefrequency in the manufacturing process, thereby resulting insimplification of the control system.

As has been described, in the case of the present embodiment, even ifthe beam spot has an offset in a first region where one side wall 201ais wobbled as illustrated in FIG. 16, it is possible to correct theoffset in a second region where no side wall is wobbled.

Besides, since wobbles are shaped with curves, in the case where theoptical disk is produced with the use of resin, mold flow into the moldis enhanced, thereby improving moldability.

Furthermore, since the wobbles are shaped with curves, high frequencynoises are hardly generated when address information is read out fromthe regions of the wobbles (the first regions). As a result, the addressinformation is read out with precision. This is very importantespecially in the case where address information is recorded only inspecific portions, as the present application.

Third Embodiment

The following description will explain still another embodiment of anoptical disk substrate of the present invention, while referring to FIG.17.

As to an optical disk substrate 205 of the present embodiment,characteristics, substrate materials, and a manufacturing processthereof are the same as those for the optical disk substrate 205 of thesecond embodiment, whereas a groove depth (land height) thereof isdifferent.

The groove depth (land height) of the optical disk substrate 205 is inthe vicinity of λ/6n (index of refraction of the substrate: n, recordingwavelength: X). The groove depth (land height) is changed by changing anetching ratio, changing etching conditions, setting a groove depth (landheight) of the stamper 210 in the vicinity of λ/6n, or changing moldingconditions.

In the case where the groove depth (land height) of the optical disksubstrate 205 is λ/6n, crosstalk between tracks (mixture of noises fromtrack signals of adjusting tracks) is reduced, thereby resulting in thathigh densification is enabled.

Fourth Embodiment

The following description will explain still another embodiment of anoptical disk substrate of the present invention, while referring to FIG.17.

As to an optical disk substrate 205 of the present embodiment,characteristics, substrate materials, and a manufacturing processthereof are the same as those for the optical disk substrate 205 of thesecond embodiment, whereas a groove depth (land height) thereof isdifferent.

The groove depth (land height) of the optical disk substrate 205 is inthe vicinity of λ/8n (index of refraction of the substrate: n, recordingwavelength: λ) . The groove depth (land height) is changed by changingan etching ratio, changing etching conditions, setting a groove depth(land height) of the stamper 210 in the vicinity of λ/8n, or changingmolding conditions.

In the case where the groove depth (land height) of the optical disksubstrate 205 is in the vicinity of λ/8n, the tracking signal ismaximized, thereby causing track following operations to be stabilized.

Fifth Embodiment

The following description will explain still another embodiment of anoptical disk substrate of the present invention, while referring to FIG.17.

As to an optical disk substrate 205 of the present embodiment,characteristics, substrate materials, and a manufacturing processthereof are the same as those for the optical disk substrate 205 of thefirst embodiment, whereas a groove depth (land height) thereof isdifferent.

The groove depth (land height) of the optical disk substrate 205 is inthe vicinity of λ/10n (index of refraction of the substrate: n,recording wavelength: λ). The groove depth (land height) is changed bychanging an etching ratio, changing etching conditions, setting a groovedepth (land height) of the stamper 210 in the vicinity of λ/10n, orchanging molding conditions.

In the case where the groove depth (land height) of the optical disksubstrate 205 is in the vicinity of λ/10n, a reproduction signal is madegreater, thereby having stable reproduction signal characteristics.

Sixth Embodiment

The following description will explain still another embodiment of anoptical disk substrate of the present invention, while referring to FIG.17.

As to an optical disk substrate 205 of the present embodiment,characteristics, substrate material, and a manufacturing process thereofare the same as those for the optical disk substrate 205 of the firstembodiment, whereas a groove depth (land height) thereof is different.

The groove depth (land height) of the optical disk substrate 205 is notless than λ/3n (index of refraction of the substrate: n, recordingwavelength: λ). The groove depth (land height) is changed by changing anetching ratio, changing etching conditions, setting a groove depth (landheight) of the stamper 210 not less than λ/3n, or changing moldingconditions.

In the case where the groove depth (land height) of the optical disksubstrate 20S is not less than λ/3n, crosserase (erasing informationrecorded in adjacent tracks by mistake during erasing operations) isavoidable even in the case where an intensity of the light beam is high.As a result, the intensity control of the light beam is made easy, whilethe erasing operations are stabilized.

Seventh Embodiment

The following description will explain an embodiment of an optical diskof the present invention, while referring to FIG. 21.

As illustrated in FIG. 21, the optical disk of the present embodimenthas a construction in which a magneto-optical recording layer 228a andan overcoat layer 229 are successively stacked on any one of the opticaldisk substrates 205 of the second through sixth embodiments. Themagneto-optical recording layer 228a, not shown, is constituted by alight-transmitting dielectric layer, a magnetic layer, a protectivelayer and a reflection layer, and the magnetic layer is made of arare-earth-metal-transition-metal alloy selected from, for example,DyFeCo, TbFeCo, DyTbFeCo, GdTbFe, GdTbFeCo, etc.

The magnetic layer has the property of exhibiting perpendicularmagnetization within the range from room temperature to the Curie Point.

In the above-mentioned arrangement, information recording is carried outin the following processes. First, (1) the temperature of the magneticlayer is raised to the vicinity of the Curie Point by applying a laserbeam so that the magnetization of the magnetic layer becomes zero or themagnetization is inverted upon application of recording magnetization,and in this state, the magnetization of the magnetic layer is alignedupward by applying, for example, upward recording magnetization.Thereafter, (2) in the same manner, the temperature of the magneticlayer is raised to the vicinity of the Curie Point by applying a laserbeam so that the magnetization of the magnetic layer becomes zero or themagnetization is inverted upon application of recording magnetization,and in this state, the magnetization of the magnetic layer is aligneddownward by applying the opposite-direction recording magnetization,that is, downward recording magnetization. Thus, information isrecorded.

Here, in actual processes, either of the light-modulation recordingmethod using a modulated laser light beam or the magnetic-fieldmodulation recording method using a modulated recording magnetic fieldcan be adopted.

Consequently, an optical disk (a magneto-optical disk), which enablesoverwriting operations of not less than 1 million times, can beachieved.

Eighth Embodiment

The following description will explain another embodiment of an opticaldisk of the present invention, while referring to FIG. 22.

As illustrated in FIG. 22, the optical disk of the present embodimenthas a construction in which a phase-change-type layer 228b and anovercoat layer 229 are successively stacked on any one of the opticaldisk substrates 205 of the second through sixth embodiments. Thephase-change-type recording layer 228b, not shown, is constituted by alight-transmitting dielectric layer, a recording layer, a protectivelayer and a reflection layer. The recording layer is made of aphase-change-type recording material, such as GeSbTe.

In the above-mentioned arrangement, when recording is carried out, ahigh-power laser light beam is applied so that the recording layerattains an amorphous state, and then a low-power laser light beam isapplied so that the recording layer attains a crystal state; thus, therecording is complete.

Consequently, it is possible to achieve a phase-change-type optical diskwhich enables an overwriting operation by using only a laser light beam.

Ninth Embodiment

The following description will explain another embodiment of an opticaldisk of the present invention, while referring to FIG. 23.

As illustrated in FIG. 23, the optical disk of the present embodimenthas a construction in which a magneto-optical recording layer 228c andan overcoat layer 229 are successively stacked on any one of the opticaldisk substrates 205 of the second through sixth embodiments.

The magneto-optical recording layer 228c, not shown, is constituted by alight-transmitting dielectric layer, a reproducing magnetic layer, arecording magnetic layer and a reflection layer, which are stacked inthis order. The reproducing magnetic layer is made of arare-earth-metal-transition-metal alloy selected from, for example,GdFeCo, GdDyFeCo, etc., and the recording magnetic layer is made of arare-earth-metal-transition-metal alloy selected from, for example,DyFeCo, TbFeCo, DyTbFeCo, GdTbFe, GdTbFeCo, etc.

The reproducing magnetic layer has the property of exhibiting in-planemagnetization within the range from room temperature to a predeterminedtemperature and of exhibiting perpendicular magnetization above thepredetermined temperature, and the recording magnetic layer has theproperty of exhibiting perpendicular magnetization within the range fromroom temperature to the Curie Point.

In the above-mentioned arrangement, upon recording, the same processesas described in the seventh embodiment are carried out, and uponreproducing, the following processes are carried out. When a light beamis applied onto the reproducing magnetic layer, the temperaturedistribution of the irradiated portion has a Gaussian distribution;therefore, only an area smaller than the light-beam diameter has atemperature rise. In accordance with this temperature rise, themagnetization of the temperature-rise portion is shifted from in-planemagnetization to perpendicular magnetization. In other words, themagnetization direction of the recording magnetic layer is copied ontothe reproducing magnetic layer due to an exchange coupling between thetwo layers, that is, the reproducing magnetic layer and the recordingmagnetic layer. When the temperature-rise portion is shifted fromin-plane magnetization to perpendicular magnetization, only thetemperature-rise portion comes to exhibit the magneto-optical effect,and information, recorded on the recording magnetic layer, is reproducedin accordance with light beam reflected from the temperature-riseportion.

Thereafter, when the light beam is shifted to reproduce the nextrecording bit, the temperature of the previously reproduced portiondrops so that a transition from perpendicular magnetization to in-planemagnetization takes place. Accordingly, the temperature-drop portion nolonger exhibits the magneto-optical effect so that the magnetization,recorded on the recording magnetic layer, is masked by the in-planemagnetization of the reproducing magnetic layer and is no longerreproduced. This makes it possible to eliminate the intervention ofsignals from adjacent bits that tends to cause noise.

As described above, in the optical disk of the present embodiment, onlythe area having a temperature not less than the predeterminedtemperature is subjected to the reproducing operation; thus, it becomespossible to reproduce a recording bit that is smaller than the diameterof a light beam, and consequently to improve the recording density to agreat degree.

Note that instead of the foregoing optical disk, an optical disk asfollows may be used: a dielectric layer is provided between areproducing magnetic layer and a recording magnetic layer, and uponreproducing, the reproducing magnetic layer is subjected to thereproducing operation by the use of a leakage magnetic field from therecording magnetic layer.

Tenth Embodiment

The following description will explain an embodiment of an opticalrecording and reproducing method of an optical disk of the presentinvention, while referring to FIG. 16.

In any one of the optical disks of the seventh through ninthembodiments, information recording can be carried out with respect toboth the first and second regions of the groove 201 and/or land 202, thefirst regions being regions wherein the wobbled side walls 201a areformed while the second regions being regions wherein the non-wobbledside walls 201b are formed. However, by recording information only inthe second regions wherein the non-wobbled side walls 201b are formed,the recording density is lowered, but more significantly, the groovesand/or lands are caused to have uniform widths, respectively, inportions where information is recorded. As a result, the reflectance ismade uniform, and information reproduction signals are stabilized.

Furthermore, since it is allowed to raise the wobble frequencies in thefirst regions to a level as high as the information recordingfrequencies in the second regions, the size of each first region can bereduced.

Note that a track to which the recording/reproduction-use light spot 204is made to follow, either a groove 201 or a land 202, is easilydesignated just by inverting a polarity of the tracking signal.

(1) As has been discussed so far, the optical disk substrate of thepresent invention on which tracking-use grooves and lands are providedhas (i) a first region where one of side walls of each groove or land iscurving in accordance with address information, and (ii) a second regionwhere no side wall is wobbled.

With this arrangement, even when the beam spot has an offset in thefirst region, the offset can be corrected in the second region.

Besides, by recording information only in the second regions, thegrooves and the lands in information recording areas are made to haveuniform widths, respectively. Therefore, the reflectance is madeuniform, thereby stabilizing information reproduction signals.Furthermore, in this case, since the first regions in which the addressinformation is recorded and the second regions in which information isrecorded are separately provided, there is no need to set the wobblefrequency considerably lower than the recording frequency. Therefore, byraising the wobble frequency of the wobbled side wall in the firstregion to a level as high as the recording frequency for information inthe second region, the size of the first region can be reduced.

In addition, since wobbles are shaped with curves, in the case where theoptical disk is produced with the use of resin, mold flow is enhanced,thereby improving moldability.

Furthermore, since the wobbles are shaped with curves, high frequencynoises are hardly generated when address information is read out fromthe regions of the wobbles (the first regions). As a result, the addressinformation is read out with precision. This is very importantespecially in the case where address information is recorded only inspecific portions, as the present application.

(2) It is preferable that the optical disk substrate has a groove depthin the vicinity of λ/6n, where an index of refraction of the substrateis n while a recording wavelength is λ.

With this arrangement, crosstalk between tracks (mixture of noises fromtrack signals of adjusting tracks) is reduced, thereby resulting in thathigh densification is enabled.

(3) It is preferable that the optical disk substrate has a groove depthin the vicinity of λ/8n, where an index of refraction of the substrateis n while a recording wavelength is λ.

With this arrangement, the tracking signal is maximized, thereby causingtrack following operations to be stabilized.

(4) It is preferable that the optical disk substrate has a groove depthin the vicinity of λ/10n, where an index of refraction of the substrateis n while a recording wavelength is λ.

With this arrangement, a reproduction signal is made greater, therebyhaving stable reproduction signal characteristics.

(5) It is preferable that the optical disk substrate has a groove depthof not less than λ/3n, where an index of refraction of the substrate isn while a recording wavelength is λ.

With this arrangement, erasing information recorded in adjacent tracksby mistake during erasing operations (crosserase) is avoidable even inthe case where an intensity of the light beam is high. As a result, theintensity control of the light beam is made easy.

(6) An optical recording and reproducing method of the presentinvention, which is a method with respect to an optical recording mediumhaving a plurality of lands and grooves having first regions where onlyone side wall is wobbled in accordance with address information andsecond regions where no wide wall is wobbled, is characterized incomprising the step of carrying out at least one among informationrecording, reproducing, and erasing operations with respect to onlysecond regions.

With this arrangement, the grooves and/or lands are caused to haveuniform widths, respectively, in portions where information is recorded.As a result, the reflectance is made uniform, and informationreproduction signals are stabilized.

Furthermore, since the first regions where address information isrecorded and the second regions where information is recorded areseparately provided, there is no need to set the wobble frequency of thewobbled side wall considerably lower than the recording frequency forrecording information. Therefore, it is allowed to raise the wobblefrequency in the first regions to a level as high as the informationrecording frequencies in the second regions, and the size of each firstregion can be reduced.

The present invention should not be limited to the above embodimentswhich are described using an example wherein an optical disk is used asthe optical recording medium, and needless to say, the same effect isachieved in the case where an optical card or an optical tape is used.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An optical information recording and reproducingdevice for the use with respect to an optical recording medium, saidoptical recording medium having a plurality of lands and grooves betweenthe lands, each of the lands and the grooves serving as a track on whicha light beam is projected for recording, reproducing, and erasinginformation, wherein each track has at least one wobble section so thataddress information is recorded therein, the wobble section having adispersively wobbled side wall of either the groove or the land, saidoptical information recording and reproducing device comprising:aphotodetector for detecting reflected light obtained by projecting alight beam on said optical recording medium; and an operational unit fordetecting a tracking signal in accordance with a signal supplied fromsaid photodetector and extracting wobble frequency components due to thewobble sections out of the tracking signal.
 2. An optical informationrecording and reproducing device, for the use with respect to an opticalrecording medium, said optical recording medium having a plurality oflands and grooves between the lands, each of the lands and the groovesserving as a track on which a light beam is projected for recording,reproducing, and erasing information, wherein each track has at leastone wobble section so that address information is recorded therein, thewobble section having a dispersively wobbled side wall of either thegroove or the land, said optical information recording and reproducingdevice comprising:a photodetector for detecting a quantity of reflectedlight obtained by projecting a light beam on said optical recordingmedium; and an operational unit for detecting changes in the quantity ofthe reflected light and extracting wobble frequency components due tothe wobble section.
 3. A method for manufacturing an optical recordingmedium, said optical recording medium having a plurality of lands andgrooves between the lands, each of the lands and the grooves serving asa track on which a light beam is projected for recording, reproducing,and erasing information, wherein each track has at least one wobblesection so that address information is recorded therein, the wobblesection having a dispersively wobbled side wall of either the groove orthe land, said method comprising the steps of:(a) providing aphotosensitive material over a substrate; and (b) selectively exposingthe photosensitive material in a shape of the wobble section, byprojecting two light beams with a distance therebetween in a directionorthogonal to a lengthwise direction of the track and swinging one ofthe two light beams in the direction orthogonal to the lengthwisedirection of the track.